My USACO Analysis:Friday the Thirteenth

This is a typical Brute Force.There's nothing to say because this is so easy!All you need is to notice the details.

program friday(input,output);
const
  monthday:array[1..12]of byte=(3,0,3,2,3,2,3,3,2,3,2,3);
var
  count:array[0..6]of integer;
  years,year,month,weekday:integer;
function leap(y:integer):boolean;
  begin
    if y mod 100=0 then
      if y mod 400=0 then leap:=true else leap:=false
    else
      if y mod 4=0 then leap:=true else leap:=false;
  end;
begin
  assign(input,'friday.in');
  reset(input);
  readln(input,years);
  close(input);

  fillchar(count,sizeof(count),0);
  weekday:=6;
  for year:=1900 to 1899+years do
    for month:=1 to 12 do begin
      inc(count[weekday]);
      if month=2 then
        weekday:=weekday+ord(leap(year))
      else
        weekday:=weekday+monthday[month];
      weekday:=weekday mod 7;
    end;

  assign(output,'friday.out');
  rewrite(output);
  write(output,count[6]);
  for weekday:=0 to 5 do
    write(output,' ',count[weekday]);
  writeln(output);
  close(output);
end.

To download the PASCAL source file:<a href=http://www1.51ok.com/down.do?85FA5DFA93D8E290AA9CFFADC67D36B7>friday.pas</a>